Hopefully not. I hate having to go through the extra step to install and play my games if I already bought the damn CD. Like when I bought Shogun 2: TW, expecting to go home, install and play it, and instead had to wait through half a day of Steam deciding that it had to download the whole damn game again even though I just installed it off the CD. F*** that pissed me off.

Bethesda's not been really big on DRM or anything in the past (you can run both Morrowind and Oblivion from an ISO without any emulation), so hopefully that will continue to be the case.

Yes, it has been confirmed that Skyrim will be a Steam Powered/Steamworks game. What this means is that it's necessary to have Steam installed on your system. When you go to install the game, you will be prompted to download and install Steam if you don't already have it.

Some Steam Pros:
1. Auto updating/patching to the latest version of the game.
2. Steam Cloud.
Some Steam Cons:
1. Auto updating/patching to the latest version of the game (this can "break" your game if you're running mods. In some cases mod authors have to update their mods to make them compatible with the latest version of the game. Fortunately this auto-updating feature can be disabled in Steam's options).
2. You must have Steam installed on your system whether you like it or not for Steam Powered games to run.
3. While you can initially install Steam itself on any hard drive/partition you want to, thereafter you are forced to install all Steam Powered games on the same hard drive. Running out of disc space is a common issue, especially for those of us who have smaller solid state drives. There are workarounds though: Symlinks, also described here, Steamtool, which utilizes NTSF junctions, Game Save Manager, etc, allow you to spread games out across multiple hard drives, but as I said, these are all workarounds and a pain in the ass.

I've personally never heard of anyone having any performance issues directly related to running Steam (well, aside from the normal performance issues that can result from too many non-essential applications "running in the background" when you boot-up your PC). You can play Skyrim with Steam in "off-line mode" (set in Steam's options settings). I never do this myself so don't know if Steam is actually still running in the background while playing?

If you haven't already, to help performance, disable non-essential applications, perform disc clean-up, defrag your hard drive(s) and update your video card(s) drivers. Then install Steam and see how it runs....